Display device having improved properties

ABSTRACT

An image display device having improved properties, comprising an image display panel, heat dispersion material positioned proximate to the image display panel, an open frame positioned proximate to the heat dispersion material opposite the image display panel, and a plurality of electronic components engaging the open frame, the image display device exhibits a support factor of less than about 375 mm-W/m° K.

RELATED APPLICATION

This application is a continuation-in-part of copending and commonlyassigned U.S. patent application having Ser. No. 11/167,935, entitled“Optimized Frame System For A Display Device,” filed in the names ofShives et al. on Jun. 27, 2005, the disclosure of which is incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a display device, such as a plasmadisplay panel (PDP), a liquid crystal display (LCD), and the like,having improved luminosity, decreased image sticking and improvedtemperature uniformity, occasioned by a unique support structure for thedevice.

BACKGROUND OF THE ART

A plasma display panel is a display apparatus which contains a pluralityof discharge cells, and is constructed to display an image by applying avoltage across electrodes discharge cells thereby causing the desireddischarge cell to emit light. A panel unit, which is the main part ofthe plasma display panel, is fabricated by bonding two glass base platestogether in such a manner as to sandwich a plurality of discharge cellsbetween them.

In a plasma display panel, each of the discharge cells which are causedto emit light for image formation generate heat and each thusconstitutes a source of heat, which causes the temperature of the plasmadisplay panel as a whole to rise. The heat generated in the dischargecells is transferred to the glass forming the base plates, but heatconduction in directions parallel to the panel face is difficult becauseof the poor thermal spreading properties of the glass base platematerial.

In addition, the temperature of a discharge cell which has beenactivated for light emission rises markedly, while the temperature of adischarge cell which has not been activated does not rise as much.Because of this, the panel face temperature of the plasma display panelrises locally in the areas where an image is being generated. Moreover,a discharge cell activated in the white or lighter color spectragenerate more heat than those activated in the darker color spectra.Thus, the temperature of the panel face differs locally depending on thecolors generated in creating the image. These localized temperaturedifferentials can accelerate thermal deterioration of affected dischargecells, often referred to as “burn-in” or “image-sticking,” dependingupon their level of permanency, unless measures are taken to amelioratethe differences. Additionally, when the nature of the image on thedisplay changes, the location for localized heat generation changes withthe image.

Further, since the temperature difference between activated andnonactivated discharge cells can be high, and the temperature differencebetween discharge cells generating white light and those generatingdarker colors can also be high, a stress is applied to the panel unit,causing the conventional plasma display panel to be prone to cracks andbreakage.

When the voltage to be applied to the electrodes of discharge cells isincreased, the brightness of the discharge cells increases but theamount of heat generation in such cells also increases. Thus, thosecells having large voltages for activation become more susceptible tothermal deterioration and tend to exacerbate the breakage problem of thepanel unit of the plasma display panel. Moreover, the luminosity of thepanel can also suffer as panel temperature rises, especially whentemperature is not uniformly distributed.

The backlights for LCD displays, such as LEDs (light emitting diodes),CCFLs (cold cathode fluorescent light or lamp) and FFPs (flatfluorescent light or lamp), present similar issues with respect to heatgeneration as do emissive displays, such as PDP's.

The use of so-called “high orientation graphite film” as thermalinterface materials for plasma display panels to fill the space betweenthe back of the panel and a heat sinking unit to even out localtemperature differences is suggested by Morita, Ichiyanagi, Ikeda,Nishiki, Inoue, Komyoji and Kawashima in U.S. Pat. No. 5,831,374.However, the disclosure is centered on the use of pyrolytic graphite asthe graphitic material and makes no mention of the use or distinctadvantages of sheets of compressed particles of exfoliated graphite. Inaddition, the use of a heavy aluminum heat sinking unit is a criticalpart of the Morita et al. invention. In addition, U.S. Pat. No.6,482,520 to Tzeng discloses the use of sheets of compressed particlesof exfoliated graphite as heat spreaders (referred to in the patent asthermal interfaces) for a heat source such as an electronic component.Indeed, such materials are commercially available from Advanced EnergyTechnology Inc. of Lakewood, Ohio as its eGraf® SpreaderShield class ofmaterials. The graphite heat spreaders of Tzeng are positioned between aheat generating electronic component and, advantageously, a heat sink,to increase the effective surface area of the heat generating component;the Tzeng patent does not address the specific thermal issues occasionedby display devices.

Graphites are made up of layer planes of hexagonal arrays or networks ofcarbon atoms. These layer planes of hexagonally arranged carbon atomsare substantially flat and are oriented or ordered so as to besubstantially parallel and equidistant to one another. The substantiallyflat, parallel equidistant sheets or layers of carbon atoms, usuallyreferred to as graphene layers or basal planes, are linked or bondedtogether and groups thereof are arranged in crystallites. Highly orderedgraphites consist of crystallites of considerable size: the crystallitesbeing highly aligned or oriented with respect to each other and havingwell ordered carbon layers. In other words, highly ordered graphiteshave a high degree of preferred crystallite orientation. It should benoted that graphites possess anisotropic structures and thus exhibit orpossess many properties that are highly directional e.g. thermal andelectrical conductivity and fluid diffusion.

Briefly, graphites may be characterized as laminated structures ofcarbon, that is, structures consisting of superposed layers or laminaeof carbon atoms joined together by weak van der Waals forces. Inconsidering the graphite structure, two axes or directions are usuallynoted, to wit, the “c” axis or direction and the “a” axes or directions.For simplicity, the “c” axis or direction may be considered as thedirection perpendicular to the carbon layers. The “a” axes or directionsmay be considered as the directions parallel to the carbon layers or thedirections perpendicular to the “c” direction. The graphites suitablefor manufacturing flexible graphite sheets possess a very high degree oforientation.

As noted above, the bonding forces holding the parallel layers of carbonatoms together are only weak van der Waals forces. Natural graphites canbe treated so that the spacing between the superposed carbon layers orlaminae can be appreciably opened up so as to provide a marked expansionin the direction perpendicular to the layers, that is, in the “c”direction, and thus form an expanded or intumesced graphite structure inwhich the laminar character of the carbon layers is substantiallyretained.

Graphite flake which has been greatly expanded and more particularlyexpanded so as to have a final thickness or “c” direction dimensionwhich is as much as about 80 or more times the original “c” directiondimension can be formed without the use of a binder into cohesive orintegrated sheets of expanded graphite, e.g. webs, papers, strips,tapes, foils, mats or the like (typically referred to as “flexiblegraphite”). The formation of graphite particles which have been expandedto have a final thickness or “c” dimension which is as much as about 80times or more the original “c” direction dimension into integratedflexible sheets by compression, without the use of any binding material,is believed to be possible due to the mechanical interlocking, orcohesion, which is achieved between the voluminously expanded graphiteparticles.

In addition to flexibility, the sheet material, as noted above, has alsobeen found to possess a high degree of anisotropy with respect tothermal and electrical conductivity and fluid diffusion, comparable tothe natural graphite starting material due to orientation of theexpanded graphite particles and graphite layers substantially parallelto the opposed faces of the sheet resulting from very high compression,e.g. roll pressing. Sheet material thus produced has excellentflexibility, good strength and a very high degree of orientation.

Briefly, the process of producing flexible, binderless anisotropicgraphite sheet material, e.g. web, paper, strip, tape, foil, mat, or thelike, comprises compressing or compacting under a predetermined load andin the absence of a binder, expanded graphite particles which have a “c”direction dimension which is as much as about 80 or more times that ofthe original particles so as to form a substantially flat, flexible,integrated graphite sheet. The expanded graphite particles thatgenerally are worm-like or vermiform in appearance, once compressed,will maintain the compression set and alignment with the opposed majorsurfaces of the sheet. The density and thickness of the sheet materialcan be varied by controlling the degree of compression. The density ofthe sheet material can be within the range of from about 0.04 g/cm³ toabout 2.0 g/cm³. The flexible graphite sheet material exhibits anappreciable degree of anisotropy due to the alignment of graphiteparticles parallel to the major opposed, parallel surfaces of the sheet,with the degree of anisotropy increasing upon roll pressing of the sheetmaterial to increase orientation. In roll pressed anisotropic sheetmaterial, the thickness, i.e. the direction perpendicular to theopposed, parallel sheet surfaces comprises the “c” direction and thedirections ranging along the length and width, i.e. along or parallel tothe opposed, major surfaces comprises the “a” directions and thethermal, electrical and fluid diffusion properties of the sheet are verydifferent, by orders of magnitude, for the “c” and “a” directions.

While the use of sheets of compressed particles of exfoliated graphite(i.e., flexible graphite) has been suggested as thermal spreaders,thermal interfaces and as component parts of heat sinks for dissipatingthe heat generated by a heat source (see, for instance, U.S. Pat. Nos.6,245,400; 6,482,520; 6,503,626; and 6,538,892), the use of graphitematerials has heretofore been independent, and not viewed asinterrelated with other components, such as the support structures ofdisplay panels.

Conventional display devices typically utilize a thick, heavy metalsupport member (often a thick aluminum sheet, or set of multiple sheets)to which is attached both the display panel unit and associatedelectronic components, such as printed circuit boards. Heat passing fromthese electronic components contributes to uneven temperaturedistributions created on the panel unit itself, which adversely affectsthe image presented on the display panels. Typically, the panel unit isattached to the support member using a two-sided adhesive tape material.Alternatively, the panel unit is sometimes attached directly to thesupport member using a full sheet of thermally conductive adhesivematerial, which is commonly a particle-filled acrylic or silicone.

In either case, the conventional support member provides both amechanical function (i.e., for mounting the panel unit and associatedelectronics), as well as a thermal function (i.e., to help sink andspread heat generated by the panel unit and/or the associatedelectronics). Accordingly, the support member is typically fabricatedfrom a solid sheet of aluminum, on the order of about 2.0 mm thick.Expressed another way, the conventional display panel having a supportmember exhibits a support factor of about 440 mm-W/m° K or higher. Thesupport factor is determined by multiplying the thickness of the supportmember present in the display panel by its in-plane thermal conductivity(thus, a 2.0 mm sheet of aluminum has a support factor of 440 mm-W/m° K,since the in-plane thermal conductivity of the high thermal conductivityaluminum employed is 220 W/m° K). It will be recognized that, since mostmetals are relatively thermally isotropic, the in-plane thermalconductivity is not substantially different from the through-planethermal conductivity of the material.

A support member such as this can weigh about 10 pounds or more, and canbe expensive and difficult to construct, due to certain flatnessrequirements, the need for many threaded mounting features for theelectronics, and the high cost of high thermal conductivity aluminumsheet. Additionally, a frame (often made from steel or aluminum) is usedto add further mechanical support to the support member, and allow for arobust mounting means for attachment of the display panel to a wallbracket or stand unit.

Conventional display device manufacturers, especially PDP manufacturers,are under extreme pressure to reduce the cost and weight of theirexisting display solutions, while there has simultaneously been a desireto increase the brightness and luminous efficiency of the panel units.This can mean more power being sent to the display, which increases thethermal load on the system and requires additional heat dissipationcapabilities within the display units. Active cooling solutions, such asfans and/or heat pipes, are undesirable due to unreliability, noise, andthe fact that they contribute negatively to the cost and weight of thesystem. In addition to increasing brightness and luminous efficiency ofthe displays, display manufacturers are also under increasing pressureto produce larger panel sizes, which tends to increase the weight of thesupport member proportionately.

Moreover, display panels having conventional frame systems exhibitundesirably high image sticking and undesirably low luminosity,exacerbating the issues detailed above. Moreover, even thoughconventional frame systems are intended to ease thermal issues for thepanels, non-uniform temperature distribution in a display panel remainsan issue, as does the average screen temperature and the temperature inthe bottom third of the screen, where temperature-increasing graphicsoften appear.

Thus, what is desired is a light weight and cost effective frame systemfor display devices, especially one which facilitates improvedluminosity, decreases image sticking and provides superior heat transfercapabilities, yet is structurally sound enough to provide both theattachment for the panel units and associated electronics, as well asthe structural integrity for mounting and supporting the display deviceitself. The desired frame system reduces or eliminates the need for asupport member, especially one formed of high conductivity aluminum.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a framefor a display device such as a plasma display panel, a liquid crystaldisplay or the like, which is lightweight and structurally sound.

It is another object of the present invention to provide a displaydevice having improved properties, including improved luminosity,reduced image sticking, reduced average screen temperature and improvedtemperature uniformity.

Still another object of the present invention is to reduce the screentemperature of a display panel in the bottom third of the panel.

Another object of the present invention is to provide a frame for adisplay device which is disposed between the heat spreading element ofthe display device and the control systems, which can be printed circuitboards, of the display device.

Yet another object of the present invention is to provide a frame for adisplay device that includes a perimeter edge providing structuralintegrity to the display device.

Another object of the present invention is to provide a frame for adisplay device having an internal aperture to facilitate heat transferand dissipation by the heat dispersion material within the displaydevice.

Still another object of the present invention is to provide a frame fora display device comprising steel.

These objects, and others which will be apparent to the skilled artisanupon reading the following description, can be achieved by providing aimage display device comprising an image display panel unit, heatdispersion material positioned proximate to the image display panel andhaving an in-plane thermal conductivity of at least about 250 W/m° K, anopen frame positioned proximate to the heat dispersion material oppositethe image display panel, a support member providing the unit with asupport factor less than about 375 mm-W/m° K, and a plurality ofelectronic components such as printed circuit boards engaging the openframe. More preferably, the support member provides a support factorless than about 150 mm-W/m° K, and in the most preferred embodiment thesupport member provides a support factor of 0 mm-W/m° K; that is, thesupport member has been eliminated altogether.

The open frame can be comprised of steel and can be adhesively bonded tothe heat dispersion material and/or the support member, when present.The open frame can include a height and a width wherein the heatdispersion material substantially spans the height and the width.Additionally, a first cross support can span the open frame and aplurality of second printed circuit boards can engage the first crosssupport. Additionally a second cross support can span the open framewherein at least one of the second printed circuit boards engages thesecond cross support. While such an arrangement for the frame ispreferred, other similar arrangements, such as two “I”-shaped pieces,reminiscent of the Roman numeral II, can also be employed as the framestructure.

When a support member is present, the heat dispersion material ispreferably positioned between the panel unit and the support member.Alternatively, support member can be positioned proximate to the displaypanel unit, between the heat dispersion material and the panel unit,provided the support member is sufficiently thin and/or thermallyconductive to permit effective heat transfer from the display panel unitto the heat dispersion material.

In another embodiment, the image display panel includes an image displayside and the heat dispersion material is positioned proximate to theimage display panel opposite the image display side. A perimeter frameis positioned proximate to the heat dispersion material opposite theimage display panel wherein the perimeter frame includes a top, abottom, a first side, and a second side. A plurality of printed circuitboards engages the perimeter frame. The top, bottom, first side, andsecond side of the perimeter frame define an aperture wherein the heatdispersion material substantially spans the aperture and can engage thetop, bottom, first side and second side of the perimeter frame. Theimage display panel can be a plasma display panel or a liquid crystaldisplay panel, while the heat dispersion material can be composed ofgraphite.

In another embodiment the image display device includes an image displaypanel positioned proximate to heat dispersion material. A frame ispositioned proximate to the heat dispersion material and opposite theimage display panel. The frame includes a height, a width, and anaperture substantially spanning the height and the width. A plurality ofprinted circuit boards engages the frame and is substantially alignedwithin the frame, and can be positioned to overlap the aperture.

Where a support member is present, it is generally configured as asheet, and it is positioned against the frame, generally between theframe and the display panel unit. The support member, when present, cancomprise a metal having a thermal conductivity lower than thatpreviously thought sufficient to provide effective heat dissipation in adisplay panel, even one utilizing a graphite or other type of heatdispersion material. For instance, rather than the use of a thick sheetof high thermal conductivity aluminum, a sheet of steel having anin-plane thermal conductivity on the order of less than about 20 W/m° Kcan be employed. Since steel is substantially less expensive than highthermal conductivity aluminum, this results in substantial savings, evenif used at the same thickness levels of high thermal conductivityaluminum, 2.0 mm. Such a steel sheet would provide the unit with asupport factor of 40 mm-W/m° K. Alternatively, the support member can behigh thermal conductivity aluminum, but employed as a substantiallythinner sheet than previously thought feasible, even in a display panelutilizing a graphite or other type of heat dispersion material. Forinstance, a sheet of high thermal conductivity aluminum of a thicknessof 0.5 mm would provide a support factor of about 110 mm-W/m° K,resulting a much lighter weight structure. Of course, when the supportmember is eliminated altogether, thus the unit has a support factor of 0mm-W/m° K, both weight savings and cost savings are substantial.

As noted, the heat dispersion material employed is preferably formed ofgraphite, and is most preferably formed from sheets of compressedparticles of exfoliated graphite, commonly known as flexible graphite.Graphite is a crystalline form of carbon comprising atoms covalentlybonded in flat layered planes with weaker bonds between the planes. Bytreating particles of graphite, such as natural graphite flake, with anintercalant of, e.g. a solution of sulfuric and nitric acid, the crystalstructure of the graphite reacts to form a compound of graphite and theintercalant. The treated particles of graphite are hereafter referred toas “particles of intercalated graphite.” Upon exposure to hightemperature, the intercalant within the graphite decomposes andvolatilizes, causing the particles of intercalated graphite to expand indimension as much as about 80 or more times its original volume in anaccordion-like fashion in the “c” direction, i.e. in the directionperpendicular to the crystalline planes of the graphite. The exfoliatedgraphite particles are vermiform in appearance, and are thereforecommonly referred to as worms. The worms may be compressed together intoflexible sheets that, unlike the original graphite flakes, can be formedand cut into various shapes.

Graphite starting materials suitable for use in the present inventioninclude highly graphitic carbonaceous materials capable of intercalatingorganic and inorganic acids as well as halogens and then expanding whenexposed to heat. These highly graphitic carbonaceous materials mostpreferably have a degree of graphitization of about 1.0. As used in thisdisclosure, the term “degree of graphitization” refers to the value gaccording to the formula: $g = \frac{3.45 - {d(002)}}{0.95}$where d(002) is the spacing between the graphitic layers of the carbonsin the crystal structure measured in Angstrom units. The spacing dbetween graphite layers is measured by standard X-ray diffractiontechniques. The positions of diffraction peaks corresponding to the(002), (004) and (006) Miller Indices are measured, and standardleast-squares techniques are employed to derive spacing which minimizesthe total error for all of these peaks. Examples of highly graphiticcarbonaceous materials include natural graphites from various sources,as well as other carbonaceous materials such as graphite prepared bychemical vapor deposition, high temperature pyrolysis of polymers, orcrystallization from molten metal solutions and the like. Naturalgraphite is most preferred.

The graphite starting materials used in the present invention maycontain non-graphite components so long as the crystal structure of thestarting materials maintains the required degree of graphitization andthey are capable of exfoliation. Generally, any carbon-containingmaterial, the crystal structure of which possesses the required degreeof graphitization and which can be exfoliated, is suitable for use withthe present invention. Such graphite preferably has a purity of at leastabout eighty weight percent. More preferably, the graphite employed forthe present invention will have a purity of at least about 94%. In themost preferred embodiment, the graphite employed will have a purity ofat least about 98%.

A common method for manufacturing graphite sheet is described by Shaneet al. in U.S. Pat. No. 3,404,061, the disclosure of which isincorporated herein by reference. In the typical practice of the Shaneet al. method, natural graphite flakes are intercalated by dispersingthe flakes in a solution containing e.g., a mixture of nitric andsulfuric acid, advantageously at a level of about 20 to about 300 partsby weight of intercalant solution per 100 parts by weight of graphiteflakes (pph). The intercalation solution contains oxidizing and otherintercalating agents known in the art. Examples include those containingoxidizing agents and oxidizing mixtures, such as solutions containingnitric acid, potassium chlorate, chromic acid, potassium permanganate,potassium chromate, potassium dichromate, perchloric acid, and the like,or mixtures, such as for example, concentrated nitric acid and chlorate,chromic acid and phosphoric acid, sulfuric acid and nitric acid, ormixtures of a strong organic acid, e.g. trifluoroacetic acid, and astrong oxidizing agent soluble in the organic acid. Alternatively, anelectric potential can be used to bring about oxidation of the graphite.Chemical species that can be introduced into the graphite crystal usingelectrolytic oxidation include sulfuric acid as well as other acids.

In a preferred embodiment, the intercalating agent is a solution of amixture of sulfuric acid, or sulfuric acid and phosphoric acid, and anoxidizing agent, i.e. nitric acid, perchloric acid, chromic acid,potassium permanganate, hydrogen peroxide, iodic or periodic acids, orthe like. Although less preferred, the intercalation solution maycontain metal halides such as ferric chloride, and ferric chloride mixedwith sulfuric acid, or a halide, such as bromine as a solution ofbromine and sulfuric acid or bromine in an organic solvent.

The quantity of intercalation solution may range from about 20 to about350 pph and more typically about 40 to about 160 pph. After the flakesare intercalated, any excess solution is drained from the flakes and theflakes are water-washed. Alternatively, the quantity of theintercalation solution may be limited to between about 10 and about 40pph, which permits the washing step to be eliminated as taught anddescribed in U.S. Pat. No. 4,895,713, the disclosure of which is alsoherein incorporated by reference.

The particles of graphite flake treated with intercalation solution canoptionally be contacted, e.g. by blending, with a reducing organic agentselected from alcohols, sugars, aldehydes and esters which are reactivewith the surface film of oxidizing intercalating solution attemperatures in the range of 25° C. and 125° C. Suitable specificorganic agents include hexadecanol, octadecanol, 1-octanol, 2-octanol,decylalcohol, 1, 10 decanediol, decylaldehyde, 1-propanol, 1,3propanediol, ethyleneglycol, polypropylene glycol, dextrose, fructose,lactose, sucrose, potato starch, ethylene glycol monostearate,diethylene glycol dibenzoate, propylene glycol monostearate, glycerolmonostearate, dimethyl oxylate, diethyl oxylate, methyl formate, ethylformate, ascorbic acid and lignin-derived compounds, such as sodiumlignosulfate. The amount of organic reducing agent is suitably fromabout 0.5 to 4% by weight of the particles of graphite flake.

The use of an expansion aid applied prior to, during or immediatelyafter intercalation can also provide improvements. Among theseimprovements can be reduced exfoliation temperature and increasedexpanded volume (also referred to as “worm volume”). An expansion aid inthis context will advantageously be an organic material sufficientlysoluble in the intercalation solution to achieve an improvement inexpansion. More narrowly, organic materials of this type that containcarbon, hydrogen and oxygen, preferably exclusively, may be employed.Carboxylic acids have been found especially effective. A suitablecarboxylic acid useful as the expansion aid can be selected fromaromatic, aliphatic or cycloaliphatic, straight chain or branched chain,saturated and unsaturated monocarboxylic acids, dicarboxylic acids andpolycarboxylic acids which have at least 1 carbon atom, and preferablyup to about 15 carbon atoms, which is soluble in the intercalationsolution in amounts effective to provide a measurable improvement of oneor more aspects of exfoliation. Suitable organic solvents can beemployed to improve solubility of an organic expansion aid in theintercalation solution.

Representative examples of saturated aliphatic carboxylic acids areacids such as those of the formula H(CH₂)_(n)COOH wherein n is a numberof from 0 to about 5, including formic, acetic, propionic, butyric,pentanoic, hexanoic, and the like. In place of the carboxylic acids, theanhydrides or reactive carboxylic acid derivatives such as alkyl esterscan also be employed. Representative of alkyl esters are methyl formateand ethyl formate. Sulfuric acid, nitric acid and other known aqueousintercalants have the ability to decompose formic acid, ultimately towater and carbon dioxide. Because of this, formic acid and othersensitive expansion aids are advantageously contacted with the graphiteflake prior to immersion of the flake in aqueous intercalant.Representative of dicarboxylic acids are aliphatic dicarboxylic acidshaving 2-12 carbon atoms, in particular oxalic acid, fumaric acid,malonic acid, maleic acid, succinic acid, glutaric acid, adipic acid,1,5-pentanedicarboxylic acid, 1,6-hexanedicarboxylic acid,1,10-decanedicarboxylic acid, cyclohexane-1,4-dicarboxylic acid andaromatic dicarboxylic acids such as phthalic acid or terephthalic acid.Representative of alkyl esters are dimethyl oxylate and diethyl oxylate.Representative of cycloaliphatic acids is cyclohexane carboxylic acidand of aromatic carboxylic acids are benzoic acid, naphthoic acid,anthranilic acid, p-aminobenzoic acid, salicylic acid, o-, m- andp-tolyl acids, methoxy and ethoxybenzoic acids, acetoacetamidobenzoicacids and, acetamidobenzoic acids, phenylacetic acid and naphthoicacids. Representative of hydroxy aromatic acids are hydroxybenzoic acid,3-hydroxy-1-naphthoic acid, 3-hydroxy-2-naphthoic acid,4-hydroxy-2-naphthoic acid, 5-hydroxy-1-naphthoic acid,5-hydroxy-2-naphthoic acid, 6-hydroxy-2-naphthoic acid and7-hydroxy-2-naphthoic acid. Prominent among the polycarboxylic acids iscitric acid.

The intercalation solution will be aqueous and will preferably containan amount of expansion aid of from about 1 to 10%, the amount beingeffective to enhance exfoliation. In the embodiment wherein theexpansion aid is contacted with the graphite flake prior to or afterimmersing in the aqueous intercalation solution, the expansion aid canbe admixed with the graphite by suitable means, such as a V-blender,typically in an amount of from about 0.2% to about 10% by weight of thegraphite flake.

After intercalating the graphite flake, and following the blending ofthe intercalant coated intercalated graphite flake with the organicreducing agent, the blend is exposed to temperatures in the range of 25°to 125° C. to promote reaction of the reducing agent and intercalantcoating. The heating period is up to about 20 hours, with shorterheating periods, e.g., at least about 10 minutes, for highertemperatures in the above-noted range. Times of one half hour or less,e.g., on the order of 10 to 25 minutes, can be employed at the highertemperatures.

The thusly treated particles of graphite are sometimes referred to as“particles of intercalated graphite.” Upon exposure to high temperature,e.g. temperatures of at least about 160° C. and especially about 700° C.to 1000° C. and higher, the particles of intercalated graphite expand asmuch as about 80 to 1000 or more times their original volume in anaccordion-like fashion in the c-direction, i.e. in the directionperpendicular to the crystalline planes of the constituent graphiteparticles. The expanded, i.e. exfoliated, graphite particles arevermiform in appearance, and are therefore commonly referred to asworms. The worms may be compressed together into flexible sheets that,unlike the original graphite flakes, can be formed and cut into variousshapes.

Flexible graphite sheet and foil are coherent, with good handlingstrength, and are suitably compressed, e.g. by roll pressing, to athickness of about 0.075 mm to 3.75 mm and a typical density of about0.1 to 1.5 grams per cubic centimeter (g/cm³). From about 1.5-30% byweight of ceramic additives can be blended with the intercalatedgraphite flakes as described in U.S. Pat. No. 5,902,762 (which isincorporated herein by reference) to provide enhanced resin impregnationin the final flexible graphite product. The additives include ceramicfiber particles having a length of about 0.15 to 1.5 millimeters. Thewidth of the particles is suitably from about 0.04 to 0.004 mm. Theceramic fiber particles are non-reactive and non-adhering to graphiteand are stable at temperatures up to about 1100° C., preferably about1400° C. or higher. Suitable ceramic fiber particles are formed ofmacerated quartz glass fibers, carbon and graphite fibers, zirconia,boron nitride, silicon carbide and magnesia fibers, naturally occurringmineral fibers such as calcium metasilicate fibers, calcium aluminumsilicate fibers, aluminum oxide fibers and the like.

The above described methods for intercalating and exfoliating graphiteflake may beneficially be augmented by a pretreatment of the graphiteflake at graphitization temperatures, i.e. temperatures in the range ofabout 3000° C. and above and by the inclusion in the intercalant of alubricious additive, as described in International Patent ApplicationNo. PCT/US02/39749.

The pretreatment, or annealing, of the graphite flake results insignificantly increased expansion (i.e., increase in expansion volume ofup to 300% or greater) when the flake is subsequently subjected tointercalation and exfoliation. Indeed, desirably, the increase inexpansion is at least about 50%, as compared to similar processingwithout the annealing step. The temperatures employed for the annealingstep should not be significantly below 3000° C., because temperatureseven 100° C. lower result in substantially reduced expansion.

The annealing of the present invention is performed for a period of timesufficient to result in a flake having an enhanced degree of expansionupon intercalation and subsequent exfoliation. Typically the timerequired will be 1 hour or more, preferably 1 to 3 hours and will mostadvantageously proceed in an inert environment. For maximum beneficialresults, the annealed graphite flake will also be subjected to otherprocesses known in the art to enhance the degree expansion—namelyintercalation in the presence of an organic reducing agent, anintercalation aid such as an organic acid, and a surfactant washfollowing intercalation. Moreover, for maximum beneficial results, theintercalation step may be repeated.

The annealing step of the instant invention may be performed in aninduction furnace or other such apparatus as is known and appreciated inthe art of graphitization; for the temperatures here employed, which arein the range of 3000° C., are at the high end of the range encounteredin graphitization processes.

Because it has been observed that the worms produced using graphitesubjected to pre-intercalation annealing can sometimes “clump” together,which can negatively impact area weight uniformity, an additive thatassists in the formation of “free flowing” worms is highly desirable.The addition of a lubricious additive to the intercalation solutionfacilitates the more uniform distribution of the worms across the bed ofa compression apparatus (such as the bed of a calender stationconventionally used for compressing (or “calendering”) graphite wormsinto flexible graphite sheet. The resulting sheet therefore has higherarea weight uniformity and greater tensile strength. The lubriciousadditive is preferably a long chain hydrocarbon, more preferably ahydrocarbon having at least about 10 carbons. Other organic compoundshaving long chain hydrocarbon groups, even if other functional groupsare present, can also be employed.

More preferably, the lubricious additive is an oil, with a mineral oilbeing most preferred, especially considering the fact that mineral oilsare less prone to rancidity and odors, which can be an importantconsideration for long term storage. It will be noted that certain ofthe expansion aids detailed above also meet the definition of alubricious additive. When these materials are used as the expansion aid,it may not be necessary to include a separate lubricious additive in theintercalant.

The lubricious additive is present in the intercalant in an amount of atleast about 1.4 pph, more preferably at least about 1.8 pph. Althoughthe upper limit of the inclusion of lubricous additive is not ascritical as the lower limit, there does not appear to be any significantadditional advantage to including the lubricious additive at a level ofgreater than about 4 pph.

The thus treated particles of graphite are sometimes referred to as“particles of intercalated graphite.” Upon exposure to high temperature,e.g. temperatures of at least about 160° C. and especially about 700° C.to 1200° C. and higher, the particles of intercalated graphite expand asmuch as about 80 to 1000 or more times their original volume in anaccordion-like fashion in the c-direction, i.e. in the directionperpendicular to the crystalline planes of the constituent graphiteparticles. The expanded, i.e. exfoliated, graphite particles arevermiform in appearance, and are therefore commonly referred to asworms. The worms may be compressed together into flexible sheets that,unlike the original graphite flakes, can be formed and cut into variousshapes and provided with small transverse openings by deformingmechanical impact as hereinafter described.

Flexible graphite sheet and foil are coherent, with good handlingstrength, and are suitably compressed, e.g. by roll-pressing, to athickness of about 0.075 mm to 3.75 mm and a typical density of about0.1 to 1.5 grams per cubic centimeter (g/cc). From about 1.5-30% byweight of ceramic additives can be blended with the intercalatedgraphite flakes as described in U.S. Pat. No. 5,902,762 (which isincorporated herein by reference) to provide enhanced resin impregnationin the final flexible graphite product. The additives include ceramicfiber particles having a length of about 0.15 to 1.5 millimeters. Thewidth of the particles is suitably from about 0.04 to 0.004 mm. Theceramic fiber particles are non-reactive and non-adhering to graphiteand are stable at temperatures up to about 1100° C., preferably about1400° C. or higher. Suitable ceramic fiber particles are formed ofmacerated quartz glass fibers, carbon and graphite fibers, zirconia,boron nitride, silicon carbide and magnesia fibers, naturally occurringmineral fibers such as calcium metasilicate fibers, calcium aluminumsilicate fibers, aluminum oxide fibers and the like.

The flexible graphite sheet can also, at times, be advantageouslytreated with resin and the absorbed resin, after curing, enhances themoisture resistance and handling strength, i.e. stiffness, of theflexible graphite sheet as well as “fixing” the morphology of the sheet.Suitable resin content is preferably at least about 5% by weight, morepreferably about 10 to 35% by weight, and suitably up to about 60% byweight. Resins found especially useful in the practice of the presentinvention include acrylic-, epoxy- and phenolic-based resin systems,fluoro-based polymers, or mixtures thereof Suitable epoxy resin systemsinclude those based on diglycidyl ether of bisphenol A (DGEBA) and othermultifunctional resin systems; phenolic resins that can be employedinclude resole and novolac phenolics. Optionally, the flexible graphitemay be impregnated with fibers and/or salts in addition to the resin orin place of the resin. Additionally, reactive or non-reactive additivesmay be employed with the resin system to modify properties (such astack, material flow, hydrophobicity, etc.).

Alternatively, the flexible graphite sheets of the present invention mayutilize particles of reground flexible graphite sheets rather thanfreshly expanded worms, as discussed in International Patent ApplicationNo. PCT/US02/16730. The sheets may be newly formed sheet material,recycled sheet material, scrap sheet material, or any other suitablesource.

Also the processes of the present invention may use a blend of virginmaterials and recycled materials.

The source material for recycled materials may be sheets or trimmedportions of sheets that have been compression molded as described above,or sheets that have been compressed with, for example, pre-calenderingrolls, but have not yet been impregnated with resin. Furthermore, thesource material may be sheets or trimmed portions of sheets that havebeen impregnated with resin, but not yet cured, or sheets or trimmedportions of sheets that have been impregnated with resin and cured. Thesource material may also be recycled flexible graphite proton exchangemembrane (PEM) fuel cell components such as flow field plates orelectrodes. Each of the various sources of graphite may be used as is orblended with natural graphite flakes.

Once the source material of flexible graphite sheets is available, itcan then be comminuted by known processes or devices, such as a jetmill, air mill, blender, etc. to produce particles. Preferably, amajority of the particles have a diameter such that they will passthrough 20 U.S. mesh; more preferably a major portion (greater thanabout 20%, most preferably greater than about 50%) will not pass through80 U.S. mesh. Most preferably the particles have a particle size of nogreater than about 20 mesh. It may be desirable to cool the flexiblegraphite sheet when it is resin-impregnated as it is being comminuted toavoid heat damage to the resin system during the comminution process.

The size of the comminuted particles may be chosen so as to balancemachinability and formability of the graphite article with the thermalcharacteristics desired. Thus, smaller particles will result in agraphite article which is easier to machine and/or form, whereas largerparticles will result in a graphite article having higher anisotropy,and, therefore, greater in-plane electrical and thermal conductivity.

If the source material has been resin impregnated, then preferably theresin is removed from the particles. Details of the resin removal arefurther described below.

Once the source material is comminuted, and any resin is removed, it isthen re-expanded. The re-expansion may occur by using the intercalationand exfoliation process described above and those described in U.S. Pat.No. 3,404,061 to Shane et al. and U.S. Pat. No. 4,895,713 to Greinke etal.

Typically, after intercalation the particles are exfoliated by heatingthe intercalated particles in a furnace. During this exfoliation step,intercalated natural graphite flakes may be added to the recycledintercalated particles. Preferably, during the re-expansion step theparticles are expanded to have a specific volume in the range of atleast about 100 cc/g and up to about 350 cc/g or greater. Finally, afterthe re-expansion step, the re-expanded particles may be compressed intoflexible sheets, as hereinafter described.

If the starting material has been impregnated with a resin, the resinshould preferably be at least partially removed from the particles. Thisremoval step should occur between the comminuting step and there-expanding step.

In one embodiment, the removing step includes heating the resincontaining regrind particles, such as over an open flame. Morespecifically, the impregnated resin may be heated to a temperature of atleast about 250° C. to effect resin removal. During this heating stepcare should be taken to avoid flashing of the resin decompositionproducts; this can be done by careful heating in air or by heating in aninert atmosphere. Preferably, the heating should be in the range of fromabout 400° C. to about 800° C. for a time in the range of from at leastabout 10 and up to about 150 minutes or longer.

Additionally, the resin removal step may result in increased tensilestrength of the resulting article produced from the molding process ascompared to a similar method in which the resin is not removed. Theresin removal step may also be advantageous because during the expansionstep (i.e., intercalation and exfoliation), when the resin is mixed withthe intercalation chemicals, it may in certain instances create toxicbyproducts.

Thus, by removing the resin before the expansion step a superior productis obtained such as the increased strength characteristics discussedabove. The increased strength characteristics are a result of in partbecause of increased expansion. With the resin present in the particles,expansion may be restricted.

In addition to strength characteristics and environmental concerns,resin may be removed prior to intercalation in view of concerns aboutthe resin possibly creating a run away exothermic reaction with theacid.

In view of the above, preferably a majority of the resin is removed.More preferably, greater than about 75% of the resin is removed. Mostpreferably, greater than 99% of the resin is removed.

Once the flexible graphite sheet is comminuted, it is formed into thedesired shape and then cured (when resin impregnated) in the preferredembodiment. Alternatively, the sheet can be cured prior to beingcomminuted, although post-comminution cure is preferred.

Optionally, the flexible graphite sheet used to form the inventivethermal solution can be used as a laminate, with or without an adhesivebetween laminate layers. Non-graphite layers may be included in thelaminate stack, although this may necessitate the use of adhesives,which can be disadvantageous, as discussed above. Such non-graphitelayers may include metals, plastics or other non-metallics such asfiberglass or ceramics.

As noted above, the thusly-formed sheets of compressed particles ofexfoliated graphite are anisotropic in nature; that is, the thermalconductivity of the sheets is greater in the in-plane, or “a”directions, as opposed to the through-sheet, or “c” direction. In thisway, the anisotropic nature of the graphite sheet directs the heat alongthe planar direction of the thermal solution (i.e., in the “a” directionalong the graphite sheet). Such a sheet generally has a thermalconductivity in the in-plane direction of at least about 140, morepreferably at least about 200, and most preferably at least about 250W/m° K and in the through-plane direction of no greater than about 12,more preferably no greater than about 10, and most preferably no greaterthan about 6 W/m° K. Thus, the thermal solution has a thermal anistropicratio (that is, the ratio of in-plane thermal conductivity tothrough-plane thermal conductivity) of no less than about 10.

The values of thermal conductivity in the in-plane and through-planedirections of the laminate can be manipulated by altering thedirectional alignment of the graphene layers of the flexible graphitesheets used to form the thermal solution, including if being used toform a laminate, or by altering the directional alignment of thegraphene layers of the laminate itself after it has been formed. In thisway, the in-plane thermal conductivity of the thermal solution isincreased, while the through-plane thermal conductivity of the thermalsolution is decreased, this resulting in an increase of the thermalanisotropic ratio.

One of the ways this directional alignment of the graphene layers can beachieved is by the application of pressure to the component flexiblegraphite sheets, either by calendering the sheets (i.e., through theapplication of shear force) or by die pressing or reciprocal platenpressing (i.e., through the application of compaction), with calenderingmore effective at producing directional alignment. For instance, bycalendering the sheets to a density of 1.7 g/cc, as opposed to 1.1 g/cc,the in-plane thermal conductivity is increased from about 240 W/m° K toabout 450 W/m° K or higher, and the through-plane thermal conductivityis decreased proportionally, thus increasing the thermal anisotropicratio of the individual sheets and, by extension, any laminate formedtherefrom.

Alternatively, if a laminate is formed, the directional alignment of thegraphene layers which make up the laminate in gross is increased, suchas by the application of pressure, resulting in a density greater thanthe starting density of the component flexible graphite sheets that makeup the laminate. Indeed, a final density for the laminated article of atleast about 1.4 g/cc, more preferably at least about 1.6 g/cc, and up toabout 2.0 g/cc can be obtained in this manner. The pressure can beapplied by conventional means, such as by die pressing or calendering.Pressures of at least about 60 megapascals (MPa) are preferred, withpressures of at least about 550 MPa, and more preferably at least about700 MPa, needed to achieve densities as high as 2.0 g/cc.

Surprisingly, increasing the directional alignment of the graphenelayers can increase the in-plane thermal conductivity of the graphitelaminate to conductivities which are equal to or even greater than thatof pure copper, while the density remains a fraction of that of purecopper. Additionally, the resulting aligned laminate also exhibitsincreased strength, as compared to a non-“aligned” laminate.

By use of such a graphite-based heat dispersion material, the reductionof the support factor for the display panel, indeed the elimination of asupport member entirely, can be effected while still providing thenecessary mechanical support and effective heat dissipation. Inaddition, use of the reduced-support factor frame system of the presentinvention can result in improved display panel properties, includingimproved luminosity, reduced image sticking, improved temperatureuniformity, reduced average screen temperature and reduced temperatureat the bottom third of the panel. In this way, overall performance ofthe display panel is improved while at the same time saving weight andcost.

Also included is a method of making an image display device exhibitingimproved properties as discussed above. The method includes providing animage display panel, a heat dispersion material, an open frame, and atleast one printed circuit board. The method includes positioning theheat dispersion material between the image display panel and the openframe and positioning at least one electronic component such as aprinted circuit board on the open frame to control the display of animage on the image display panel. While the inclusion of one or morefans to facilitate heat dispersion is undesirable, as noted above, ifadditional heat dissipation is required, fans can be deployed about theframe for this purpose.

It is to be understood that both the foregoing general description andthe following detailed description provide embodiments of the inventionand are intended to provide an overview or framework of understandingand nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention and are incorporated in and constitute a part of thespecification. The drawings illustrate various embodiments of theinvention and together with the description serve to describe theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view showing an example of the elements ofan embodiment of an image display device made in accordance with thecurrent disclosure.

FIG. 2 is a top perspective view of the embodiment shown in FIG. 1.

FIG. 3 is a side perspective view of the embodiments shown in FIGS. 1-2.FIG. 3 shows an example of the adhesive applied to a frame.

FIG. 4 is a side perspective view similar to FIG. 3. FIG. 4 shows anexample of the heat dissipation material positioned in the frame.

FIG. 5 is a side perspective view similar to FIGS. 3-4. FIG. 5 shows theframe and heat dissipation material positioned proximate to an imagedisplay screen.

FIG. 6 is a perspective view similar to FIGS. 3-5. FIG. 6 shows printedcircuit boards positioned on the frame while the frame and heatdissipation material are positioned proximate to the image displaypanel.

FIG. 7 is a back perspective view similar to FIGS. 3-6. FIG. 7 showssupport members positioned to engage the frame while the remainingcomponents are aligned and substantially positioned proximate to oneanother.

FIG. 8 is a back perspective view similar to FIG. 7.

FIG. 9 is a back perspective view showing an alternate embodiment of adisplay device made in accordance with the current invention.

FIG. 10 is a front view of an image display device shown within a casingand having an image displayed thereon.

FIG. 11 is a back view of a frame made in accordance with the currentinvention showing an example of the lip and flange.

FIG. 12 is a back view of the frame made in accordance with the currentdisclosure. FIG. 12 shows an example of an adhesive applied to theflange of the frame.

FIG. 13 is a back view similar to FIG. 12. FIG. 13 shows heat dispersingmaterial and adhesive positioned on the flange of the frame.

FIGS. 14-16 are schematic representations of alternative embodiments ofthe frame system of the present invention, having a support factor of 0mm-W/m° K.

FIG. 17 is a photograph of the existing aluminum chassis and steelsubframe of the PDP described in Example One.

FIG. 18 is a photograph of the inventive frame system used to replacethe existing aluminum chassis and steel subframe of the PDP described inExample One.

FIG. 19 is a representation of the PDP used to conduct the experiment ofExample Two.

FIG. 20 is a representation of the white spot test pattern used in theexperiment of Example Two.

FIG. 21 is a representation of a typical IR image resulting from theexperiment of Example Two.

FIG. 22 is a chart of temperature versus time resulting from theexperiment of Example Two.

FIG. 23 is a chart of temperature versus luminosity resulting from theexperiment of Example Two.

FIG. 24 is a representation of the white spot test pattern of FIG. 20replaced by a full white pattern to evaluate image sticking used in theexperiment of Example Two.

FIG. 25 is a chart of luminosity versus time resulting from theexperiment of Example Two.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring generally now to FIGS. 1-13, an image display device is shownand generally designated by the numeral 10. The image display device 10comprises an image display panel 12 for displaying an image 14, heatdispersion material 16 positioned proximate to the image display panel12, a frame 18 positioned proximate to the heat dispersion material 16opposite the image display panel 12, and a plurality of printed circuitboards 20 engaging the frame 18. The frame 18 includes a height 22, awidth 24 and an aperture 26 substantially spanning the height 22 andwidth 24. The heat dispersion material 16 can substantially span theheight 22 and width 24 of the frame 18.

The printed circuit boards 20 can be substantially aligned within theframe 18, and can overlap a portion of the aperture 26. This alignmentfacilitates the heat dispersion material 16 to dissipate heat generatedby the printed circuit boards 20.

In a preferred embodiment the heat dispersion material 16 comprisesgraphite while the frame 18 is composed of steel. Additionally, theframe 18 can include a lip 28 positioned around the perimeter of theframe 18 and a flange 30 extending inward from the lip 28. The printedcircuit boards 20 can engage the lip 28 and/or the flange 30 in order tosecure the printed circuit boards 20 to the frame 18. The heatdispersion material 16 can also engage the flange 30 opposite theprinted circuit boards 20. As such, the heat dispersion material 16 cansubstantially span the aperture 26 of the frame 18. This facilitatesheat dispersion by the heat dispersion material 16 within the imagedisplay device 10.

The image display panel 12 can include an image display side 13 on whichthe image 14 is displayed. The image display side 13 can be seen throughthe casing 11 of the image display device as best illustrated in FIG.10.

Looking now at FIGS. 1-8, assembly of an embodiment of an image displaydevice 10 made in accordance with the current invention can be describedas follows. An adhesive 32, for example acrylic adhesive tape, can beattached to the flange 30 opposite the lip 28. The width of the adhesive32 is preferably less than the width of the flange 30 to allow room forattachment of the heat dispersion material 16 to the flange 30 of theframe 18. A second adhesive 33, such as a pressure sensitive adhesive,could be used on the inner part of the flange 30 to attach the heatdispersion material 16 to the flange 30 of the frame 18. Alternately,the adhesive 32 can substantially span the width of the flange 30,wherein the heat dispersion material 16 is attached to the frame 18 bythe adhesive 32.

In a preferred embodiment the thickness of the adhesive 32 issubstantially the same as the thickness of the heat dispersion material16. This further facilitates the positioning of the heat dispersingmaterial 16 proximate to the image display panel 12 and facilitates aproper attachment of the frame 18 to the image display panel 12.Alternately, mechanical fixtures could be used to attach the frame 18,heat dispersion material 16, and the display panel 12.

The heat dispersion material 16 could also include an adhesive (notshown) on the surface facing the image display panel 12. This adhesive,for example a pressure sensitive adhesive, can facilitate good thermalcontact between the image display panel 12 and the heat dispersionmaterial 16 to enhance the heat dissipation within the image displaydevice 10.

The combination of the frame 18 and heat dispersion material 16 could bepressure sealed to the image display panel 12. This type of sealfacilitates a proper placement of the heat dispersion material 16 to theimage display panel 12 to disperse the heat generated by the imagedisplay panel 12. Additionally this type of seal can aid the frame 18 inproperly supporting the image display panel 12. This pressure can beapplied in various ways, such as a compliant pad or a pressurized airsystem during assembly. Alternately, the heat dispersion material 16could be individually engaged to the image display panel 12 with theframe 18 subsequently engaged to the assembled combination of the imagedisplay panel 12 and the heat dispersion material 16.

Next the printed circuit boards 20 could be applied to the frame 18, orheat dispersion material 16. The printed circuit boards 20 could beattached to standoffs (not shown) as known in the art and positioned toproperly control the display of the image 14 on the image display side13 of the image display panel 12. The printed circuit boards 20 couldalso be positioned on the lip 28 or flange 30 of the frame 18.

Additionally, cross supports 34 could be attached to the frame 18. Thesecross supports 34 could be used to strengthen and stabilize the frame 18and overall image display device 10. The engagement between the crosssupports 34 and the frame 18 could include mechanical fasteners such asscrews, bolts, rivets, clips, and the like, as known in the art.

Multiple cross supports 34 could be used to add further rigidity to theframe 18 and image display device 10. These cross supports 34 couldinclude additional traversing members 36 used to add further rigidity tothe frame 18. The cross supports 34 preferably span the frame 18 and canengage the lip 28 or flange 30. The cross supports 34 and traversingmembers 36 can be comprised of, individually or in combination, steel,aluminum, and plastic. The cross supports 34 could be used to engage thecasing 11 and secure the casing 11 as part of the image display device10. In an alternate embodiment a plurality of second printed circuitboards 21 could be attached to the cross supports 34 or traversingmembers 36 to provide further controls for the image display device 10.

The printed circuit boards 20 and 21 can be spaced from the heatdispersion material 16 to allow more air movement between the printedcircuit boards 20 and 21 and the heat dispersion material to facilitateeffective heat removal from the image display device 10.

Alternately, the frame 18 can be described as an open frame 18. The openframe 18 includes an aperture 26 within its perimeter to facilitate heattransfer within the image display device 10. The frame can also bealternately described as a perimeter frame 18 wherein the perimeterframe 18 includes a top 38, bottom 40, first side 42, and second side44. The top 36, bottom 40, first side 42, and second side 44 can definethe aperture 26 and can be shaped to form the flange 30 of the perimeterframe 18.

The frame 18 could be manufactured as a single extruded piece and bent,or folded, into shape. Alternately, the frame 18 could be manufacturedin multiple pieces and mechanically assembled, such as by rivets, welds,or the like, thereby reducing the need to stamp the frame 18 from asingle sheet of material.

Referring now to FIGS. 14-16, some alternate embodiments of frame 18 areshown to provide an indication of the different formats and orientationsthat can be provided. In each case, frame 18 includes a top 38, bottom40, first side 42, and second side 44. In addition, cross supports 34and traversing members 36 are present to provide structural support toframe 18 as well as a mounting point for electronics, etc.

In order to facilitate a more complete understanding of the invention, anumber of examples are provided below. However, the scope of theinvention is not limited to the specific embodiments disclosed in theseexamples which are for purposes of illustration only. All proportionsand quantities referred to in the following examples are by weightunless otherwise stated.

EXAMPLE ONE

A 42″ commercial PDP (Hitachi Ultravision HD42T51) is thermally testedin the as-received condition. Thermal characterization of the panel isconducted using an infrared camera (IR Flexcam® infrared camera) focusedon the front of the PDP. The testing conducted is under conditions of100 % illumination (full white).

The same PDP is then dismantled and the existing aluminum chassis andsteel subframe (FIG. 17) replaced by the inventive frame as shown inFIG. 18. Thermal testing is then repeated, with results reported inTable 1. TABLE 1 Average Full White Temperature Chassis Average Rise inWeight Temperature Bottom Zone lbs Rise ° C. ° C. State of the Art 23.928.1 25.0 Optimized Frame 12.6 24.5 20.6 Improvement 11.3 3.6 4.4

As shown in Table 1, a weight reduction of 11.3 lbs is achieved and anaverage temperature reduction of 3.6° C. is achieved. This reduction intemperature is important because, as shown in Example Two, luminance andimage sticking, both important display parameters, are improved astemperature is reduced. Another unexpected benefit is that the bottomthird of the PDP, as defined by a zone within 30 mm of the bottom andextending across the full width of the panel, shows an even largeraverage temperature reduction of approximately 4.4° C. when comparedwith a conventional PDP (Table 1). Low temperatures in this region areparticularly important because this is a common area where a whitebackground can stay static for a prolonged period (such as when graphicssuch as ticker messaging, etc. are displayed), which can locallyincrease temperature and cause a reduction in luminance and an increasein image sticking.

To demonstrate the additional benefit which can be achieved by the useof fans, four cross-flow fans, Model DF25 by Dofasco Inc. are installedabout the frame, and the thermal testing repeated. The results are shownin Table 2. TABLE 2 Full White Average Temperature Rise ° C. State ofthe Art 28.1 Optimized Frame 24.5 Optimized Frame 20.5 with Fans

As can be seen in Table 2, the use of fans in the optimized frame of thepresent invention can provide an additional 4° C. of temperaturereduction.

EXAMPLE TWO

To demonstrate that lower temperatures improve luminosity and reduceimage sticking, both important display parameters, an experiment isconducted to vary the PDP screen temperature over a wide range andmeasure corresponding luminance and image sticking trends withtemperature. A PDP screen is split into three zones with, respectively,no heat spreader, a low thermal conductivity (approximately 1 W/m° K)acrylic thermal interface material bonded to the aluminum chassis, and ahigh in-plane thermal conductivity (approximately 400 W/m° K) graphiteheat spreader contacting the PDP glass, as shown in FIG. 19. A whitespot test pattern is then set up with two spots/zone, as shown in FIG.20, and the temperature of each spot measured every two minutes as thePDP panel heats up. A typical IR image is shown in FIG. 21 with a chartof temperature versus time shown in FIG. 22. The advantage of thegraphite spreader in minimizing temperature rise in the white spot areais apparent. Note also the broad range of temperatures achieved in thisexperiment, representing extremes of PDP performance.

Over the same time interval, luminosity measurements are conducted oneach of the six spots using a Minolta CA210 Luminance meter. This allowstemperature versus luminosity data to be generated with the resultantplot shown in FIG. 23. A clear correlation of temperature withluminosity is demonstrated with luminosity decreasing as temperatureincreases; however, the inventive graphite heat spreader is associatedwith higher luminosity readings by virtue of the lower temperatures (seealso Table 3). Using the equation for luminosity versus temperaturedeveloped in this experiment and substituting in the values oftemperature shown in Table 1, it can be calculated that the inventiveframe system will improve luminosity of a PDP by 5.1 candellas persquare meter (cd/m²) on average. TABLE 3 Average Average Average TimeAverage Time for White Spot Luminance for Spot to Spot Luminance toReach Temperature after 30 Visually 96% Luminance Value of after 30minutes Disappear White Background Spreader minutes ° C. cd/m² (minutes)(minutes) Graphite 37.6 324.0 9 <2 Acrylic 44.7 302.3 13 4-6 No Spreader63.0 286.6 18 12-14

The other key benefit of lower temperatures is reduced image stickingwhich is the tendency of an image to be stuck as a background is changedon the PDP screen. This is highly undesirable when a PDP is either usedas a monitor or a TV screen, as the viewer sees remnants of old images.Image sticking can be quantified in two ways. One is simply the time ittakes for a remnant image to disappear as viewed by the naked eye whenswitching the white spot pattern to a full white screen (described asbright image sticking). The other is based on the time it takes for theluminance in the white spot region to become equivalent to the luminancein the adjoining white (previously black) region.

The test conducted to evaluate image sticking is the white spot testpattern shown in FIG. 20. After approximately 30 minutes, the white spottest pattern is replaced by a full white pattern (100% illumination). Inthis test it is visually evident that the white spots immediately becomeless bright (have lower luminance) than the surrounding whitebackground, because as described above the spots are at a highertemperature, as shown in FIG. 24. As the white spots cool, theirluminance increases and eventually the spot disappears to the naked eye.This is the first measure of image sticking (time for spot to visuallydisappear). As the luminance of the white spots increase there comes apoint at which the luminance is equal to the luminance of the backgroundwhite. This is a second measure of image sticking (time for luminance tobecome equivalent). In practice, these times can be very long fornon-graphite spreaders and so for the purposes of allowing a comparison,a value of 96% relative luminosity (defined as the spot luminancereaching 96% of the luminance of the white background) is used. A plotof relative luminosity versus time is shown in FIG. 25. Table 3summarizes the time in minutes for the spots to disappear to the nakedeye and also the time for the luminance to reach a value of 96% relativeluminosity. It is clear that by both image sticking criteria, lowertemperatures result in a lower propensity for image sticking.

Thus, by the practice of the present invention, an image display panelhaving surprisingly improved properties and characteristics is provided,in addition to being of lower weight and cost. These improved propertiesand characteristics include improved luminosity as compared toconventional image display panels, reduced image sticking, improvedtemperature uniformity (that is, reduction of temperature differentialsacross the screen), reduced average screen temperature and reducedtemperature along the bottom third of the screen. These factors allcombine to provide an image display panel having a longer and moreeffective lifespan than previously anticipated.

All patents and patent applications referred to herein are incorporatedby reference.

The invention thus being described, it will obvious that it may bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the present invention and allsuch modifications as would be obvious to one skilled in the art areintended to be included in the scope of the following claims.

1. A method for improving a characteristic of an image display devicecomprising: providing an image display panel; providing a heatdispersion material having an in-plane thermal conductivity of at leastabout 250 W/m° K positioned proximate to the image display panel,wherein the image display device exhibits a support factor of less thanabout 375 mm-W/m° K.
 2. The method of claim 1, wherein the improvedcharacteristic comprises increased luminance, decreased image sticking,improved thermal properties, or combinations thereof.
 3. The method ofclaim 2, further comprising providing an open frame positioned proximateto the heat dispersion material opposite the image display panel,wherein the open frame including a height and a width, wherein the heatdispersion material is positioned so as to substantially span the heightand the width.
 4. The method of claim 2, wherein the heat dispersionmaterial comprises at least one sheet of compressed particles ofexfoliated graphite.
 5. The method of claim 2, wherein the image displaydevice exhibits a support factor of 0 mm-W/m° K.
 6. A image displaydevice having improved luminance comprising: an image display panel;heat dispersion material having an in-plane thermal conductivity of atleast about 250 W/m° K positioned proximate to the image display panel;and an open frame positioned proximate to the heat dispersion materialopposite the image display panel, wherein the image display deviceexhibits a support factor of less than about 375 mm-W/m° K.
 7. The imagedisplay device of claim 6, further including a first cross supportspanning the open frame and a plurality of second printed circuit boardsengaging the first cross support.
 8. The image display device of claim6, wherein the open frame including a height and a width, wherein theheat dispersion material substantially spans the height and the width.9. The image display device of claim 6, wherein the heat dispersionmaterial comprises at least one sheet of compressed particles ofexfoliated graphite.
 10. The image display device of claim 6, whichexhibits a support factor of 0 mm-W/m° K.
 11. The image display deviceof claim 6, which further comprises at least one fan.
 12. A imagedisplay device exhibiting decreased image sticking comprising: an imagedisplay panel; heat dispersion material having an in-plane thermalconductivity of at least about 250 W/m° K positioned proximate to theimage display panel; an open frame positioned proximate to the heatdispersion material opposite the image display panel; and a plurality ofelectronic components engaging the open frame, wherein the image displaydevice exhibits a support factor of less than about 375 mm-W/m° K. 13.The image display device of claim 12, further including a first crosssupport spanning the open frame and a plurality of second printedcircuit boards engaging the first cross support.
 14. The image displaydevice of claim 13, further including a second cross support spanningthe open frame wherein at least one of the second printed circuit boardsengages the second cross support.
 15. The image display device of claim12, wherein the open frame is composed of steel.
 16. The image displaydevice of claim 12, wherein the open frame including a height and awidth, wherein the heat dispersion material substantially spans theheight and the width.
 17. The image display device of claim 12, whereinthe heat dispersion material comprises at least one sheet of compressedparticles of exfoliated graphite.
 18. The image display device of claim12, which exhibits a support factor of 0 mm-W/m° K.
 19. A image displaydevice having improved thermal properties comprising: an image displaypanel; heat dispersion material having an in-plane thermal conductivityof at least about 250 W/m° K positioned proximate to the image displaypanel; an open frame positioned proximate to the heat dispersionmaterial opposite the image display panel; and a plurality of electroniccomponents engaging the open frame, wherein the image display deviceexhibits a support factor of less than about 375 mm-W/m° K.
 20. Theimage display device of claim 19, further including a first crosssupport spanning the open frame and a plurality of second printedcircuit boards engaging the first cross support.
 21. The image displaydevice of claim 19, further including a second cross support spanningthe open frame wherein at least one of the second printed circuit boardsengages the second cross support.
 22. The image display device of claim19, wherein the open frame is composed of steel.
 23. The image displaydevice of claim 19, wherein the open frame including a height and awidth, wherein the heat dispersion material substantially spans theheight and the width.
 24. The image display device of claim 19, whereinthe heat dispersion material comprises at least one sheet of compressedparticles of exfoliated graphite.
 25. The image display device of claim19, which exhibits a support factor of 0 mm-W/m° K.
 26. The imagedisplay device of claim 19, which further comprises at least one fan.